1. Field of the Invention
The present invention relates in general to a hard multilayer coating, and more particularly to such a hard multilayer coating that is excellent in its heat resistance and wear resistance.
2. Discussion of the Related Art
There is widely used TiAlN as a hard coating that is disposed on a surface of a body such as a tool substrate made of high-speed tool steel, cemented carbide or other material. In recent years, as disclosed in JP-2003-71610A and JP-2000-308906A (publications of unexamined Japanese Patent Applications laid open in 2003 and 2000), there are proposed TiAlCrN and TiAl(SiC)N as the hard coating for such a use.
Each of TiAlCrN and TiAl(SiC)N has a coating hardness and an oxidation initiation temperature that are higher than those of TiAlN, as shown in FIG. 7, and accordingly is excellent in its heat resistance and wear resistance. However, the oxidation initiation temperature of TiAlCrN is about 900° C., and is lower than that of TiAl(SiC)N. The coating hardness (HV0.025) of TiAl(SiC)N is about 3000, and is lower than that of TiAlCrN. That is, the hard coating still has a room to be improved, particularly, in view of the use as a coating provided to cover a substrate of a tool intended for machining a high hardness material at a high speed.